WASHINGTON (CNN) --Trying to assure the public of the safety of American beef, the U.S. Department of Agriculture is tracking the history of the animal presumed to have mad cow disease as other nations ban imported U.S. beef.

Canada announced a partial ban on U.S. beef products Wednesday, joining a growing list of countries who've stopped imports, including China, which has suspended imports of all U.S.-produced beef, according to an official with the China's General Administration of Quality Supervision, Inspection and Quarantine said.

Canadian Agriculture Minister Bob Speller said the country will continue to import boneless beef from cows slaughtered under the age of 30 months, dairy products, and cows for slaughter that are under the age of 30 months.

Canada will continue importing only those products and animals "which on the basis of scientific measures do not pose a risk," Speller told reporters at a news conference in Ottawa. The partial ban could be revised depending on what investigators find, he added.

The disease is generally not found in cows under the age of 30 months. Health officials said it is also not found in dairy products.

Dr. Brian Evans, chief veterinary officer of the Canadian Food Inspection Agency, said Canada is "putting public health first," but still acting in "the least trade restrictive manner -- because that's how we expect to be treated."

In May, a single case of mad cow disease was found in Canada. Although no other cases were found, the United States banned the import of Canadian beef for several months.

"We are sending the message to all countries around the world that measures can be taken to protect public health," he said.

Mexico, Japan and South Korea are the top three importers of American beef by volume, buying nearly three-quarters of the total, according to the U.S. Meat Export Federation Web site. Mexico imports 28 percent, Japan 27 percent and South Korea 19 percent, the site said.

The United States is the leading exporter of beef in the world, with sales totaling about $3.5 billion for 2003, according to Philip Seng, president and chief executive officer of the U.S. Meat Export Federation in Denver, Colorado.

"This would be significant if we were to lose even half our export sales," Seng said. "This would be a very debilitating development in the United States."

Meanwhile, the FDA continues its probe into the history of the stricken cow. Wednesday, the USDA announced that the Food and Drug Administration had dispatched teams of investigators to determine any potential role of animal feed in the USDA's findings. The USDA said there is no reason to suspect that more than one cow is involved.

The sick animal came from a farm in Mabton, Washington, about 40 miles southeast of Yakima. The farm is now under quarantine.

About 4 years old, the sick cow came from a farm with two dairy operations, agriculture officials said. The cow was to be slaughtered December 9 but was culled from the herd because of paralysis that resulted from delivering a calf.

She was purchased in October 2001 when she was 2. Officials are tracing her heritage.

On Tuesday, the Department of Agriculture announced the Washington case was possibly the first instance of mad cow disease in the country. Final testing on the case will come within three to five days.

Recall issued

Agriculture Secretary Ann Veneman said Wednesday the chances of becoming sick from U.S. meat possibly tainted with the disease is "extremely low."

Veneman told CNN that product from what appears to be a sick cow "has gone into further processing plants from the initial slaughter plant, and we are now tracing that product."

She said a recall for about 10,000 pounds of meat had been issued.

"We'll be tracing that forward to see where the product went and to remove it from the food supply," Veneman said.

Veneman cautioned that the distribution of the meat to other processing plants does not mean the public is in danger.

Industry group says system working

Mad cow disease decimated the European cattle industry in the 1990s, where its human variant, Creutzfeldt-Jakob disease, has been linked to more than 100 deaths.

The first confirmed case in North America appeared in Alberta, Canada, in May.

The National Cattlemen's Beef Association promised to support aggressive steps to eliminate any trace of BSE from the U.S. cattle population and said the system had worked in tracking down the case in Washington.

But an industry critic said the case is likely "the tip of an invisible iceberg."

A South Korean butcher weighs a block of imported beef at his shop in Seoul on Wednesday.

"There are more cases, no doubt about it," warned John Stauber, author of "Mad Cow USA."

Stauber said the fact that it took so long to find a U.S. case only underscores weakness in the testing system.

"In Europe and Britain, they test virtually every beef animal for mad cow," Stauber said. "That's what we should be doing in the United States.

"The public should be very concerned about this. The real problem here in the United States is that we have not taken the measures that we need to take to deal with this disease."